The present invention relates to a torque adjustment device and more particularly to a torque adjustment device used in an electric drill.
In torque adjustment devices for electric drills used in general, ones disclosed in Japanese Utility Model Laid Open Application No. 59-183764 and Japanese Patent Publication No. 57-61554 are extensively known.
In a device shown in Japanese Utility Model Laid Open Application No. 59-183764, a groove is formed in an end face of a clutch adjustment handle, and a clutch mounting plate having a projection engageable with the groove is provided on the end face of the clutch adjustment handle. The clutch adjustment handle is rotated so that the clutch adjustment handle is moved in an axial direction corresponding to a height of the projection.
In the device shown in Japanese Patent Publication No. 57 61554, a flat portion is provided in a slanted surface formed in a support member and the slanted surface is formed in a stepped shape. A recess into which the clutch plate is inserted is formed in the flat portion. The clutch plate is inserted into the recess to thereby determine the rotational position of the support member. The amount of compression of a clutch spring for pushing the clutch plate causes the adjustment of the retainer force of an inwardly toothed gear through steel balls, thereby adjusting the output torque.
However, in the device disclosed in Japanese Utility Model Laid Open Application No. 59-183764, since the clutch adjustment handle is moved in the axial direction, it is necessary to provide a gap between the clutch adjustment handle and the housing, resulting in worse appearance. Also, since the compression amount of the spring is changed due to the movement, it is difficult to set a maximum torque. Furthermore, since the clutch adjustment handle is made of resin and the clutch mounting plate is made of steel, the groove of the clutch adjustment handle is worn out, resulting in disabling the positioning.
On the other hand, in the device disclosed in Japanese Patent Publication No. 57-61554, when the lock condition is kept (i.e., the spring is kept under the compressed condition), the clutch plate is inserted into the recess of the flat portion. Accordingly, in order that the clutch plate rides over the recess, it is impossible to keep the spring under the sufficiently compressed condition under the lock condition. It is therefore impossible to perform fine adjustment of the torque, and it is difficult to set a maximum torque. The force for rotating the support member is different between the condition where the clutch spring is compressed and the condition where the clutch spring is not compressed. Accordingly, the rotational force is not uniform. Furthermore, although the click feeling is obtained under the compression condition, there is no click feeding under no compression. It is therefore difficult to judge whether or not the desired position is obtained. Also, the support claws of the clutch plate are strongly pushed against the flat portion of the slanted surface by the clutch spring. Under this condition, when the support member is rotated, the support claws ride over the flat portion under the condition where the support claws are strongly pushed against the flat portion. In general, the support member is made of resin and the clutch plate is made of steel. Accordingly, the flat portion of the slanted surface is worn out or deformed, resulting in poor durability.